1. Field of the Invention
The present invention generally relates to integrated circuit chip packaging, and, more specifically, to absorbing excess under-fill flow with a solder trench.
2. Description of the Related Art
Consumer demand for increasingly smaller electronic devices has grown dramatically, primarily in the form of thinner mobile phones and lighter laptops. Continued miniaturization of consumer electronic devices has generated a demand for thinner integrated circuit (IC) packages that incorporate the processing devices and memory devices that run consumer electronic devices. However, limits exist on what methods may be employed by IC package fabricators to further reduce the height of IC packages and yet continue producing IC packages precisely to the required specifications.
One common problem in the art is attempting to control the height of a “solder dam” when producing thin IC packages. A solder dam is formed around an IC that is mounted on a packaging substrate, and may be analogized to the walls of an above-ground pool, wherein the walls of the pool contain the water in the pool and prevent people outside the pool from getting wet. In the instant case, a solder dam contains “under-fill” and protects chip capacitors or other structures mounted on the packaging substrate from the flow of excess under-fill within the package. As is well-known, under-fill is used to support and secure various parts of the IC package.
During fabrication, a stencil is placed on a surface of a packaging substrate, and the holes of the stencil are used to precisely deposit solder paste onto targeted areas of the surface of the substrate. Because the solder dam protrudes above the surface of the packaging substrate, if the solder dam has too much height, the stencil cannot be placed in direct contact with the substrate surface, thereby reducing the precision of solder paste deposition. Furthermore, if the solder dam is misaligned, an outcome that is more likely as the height of the solder dam increases, the solder dam may cause the stencil to be placed askew, resulting in inaccurate deposition of solder paste. As a general matter, imprecise deposition of solder paste is undesirable because improper deposition may result in incomplete electrical connections in the IC package, which could cause the IC package to malfunction or become inoperable.
As the foregoing illustrates, there is a need in the art for a more effective way to guard against the flow of under-fill within an IC package.